Exemplary embodiments of the present invention relate to a method for fabricating a magnetic tunnel junction, and more particularly, to a method for fabricating magnetic tunnel junctions having a uniform critical dimension (CD).
A dynamic random access memory (DRAM) and a flash memory device are representative of semiconductor devices. Here, the DRAM has a fast data processing speed due to easier data access, whereas the flash memory device stores nonvolatile data. Further, the DRAM periodically refreshes data, whereas the flash memory device has a slow data processing speed due to more difficult data access.
Recently, semiconductor devices combining benefits of both the DRAM and the flash memory device have been developed. An exemplary semiconductor device is a spin transfer random access memory, which uses the quantum mechanical effect, i.e., magneto resistance. The spin transfer random access memory has the easier data accessibility of the DRAM and the non-volatile data storage capacity of the flash memory device.
The spin transfer random access memory includes a magnetic tunnel junction to store data. Generally, the magneto resistance (MR) is changed depending on the magnetization direction between two ferromagnetic layers. The spin transfer random access memory senses a change in magneto resistance and reads whether data stored in the magnetic tunnel junction is 1 or 0.
FIG. 1 illustrates a plan view of a conventional magnetic tunnel junction and a sectional view taken along line of the magnetic tunnel junction.
As illustrated in FIG. 1, the magnetic tunnel junction includes a first magnetic layer 102, an insulation layer 103 and a second magnetic layer 104, which are formed on a substrate 101. The first magnetic layer 102 is a layer of which magnetization direction is fixed, and a second magnetic layer 104 is a layer of which magnetization direction is changed depending on a supply direction of current.
If the magnetization directions of the first and second magnetic layers 102 and 104 are the same, the resistance of the magnetic tunnel junction is low. If the magnetization directions of the first and second magnetic layers 102 and 104 are opposite to each other, the resistance of the magnetic tunnel junction is high. According to these characteristics, the magnetic tunnel junction reads data by supplying current between the first and second magnetic layers 102 and 104 and measuring the resistance of the magnetic tunnel junction.
Here, critical dimensions (CDs) of magnetic tunnel junctions may be changed in a process of patterning the magnetic tunnel junctions. In FIG. 1, the lateral width W1 of a first magnetic tunnel junction MTJ1 is patterned larger than the lateral width W2 of a second magnetic tunnel junction MTJ2. Also, the longitudinal width of the first magnetic tunnel junction MTJ1 is patterned larger than that of the second magnetic tunnel junction MTJ2. This is because distributions of etch plasma in the magnetic tunnel junctions MTJ1 and MTJ2 are different for each other in the process of patterning the magnetic tunnel junctions MTJ1 and MTJ2. In a case where the CDs of the magnetic tunnel junctions are different from each other, tunneling magneto resistances (TMRs) and resistances of area factors (RAs) in the magnetic tunnel junctions are different from each other and makes it difficult to read data. Here, the TMR and RA are magnetization characteristics of the magnetic tunnel junction.